Lithographic processes involve establishing image (printing) and non-image (non-printing) areas on a substrate, substantially on a common plane. When such processes are used in printing industries, non-image areas and image areas are arranged to have different affinities for printing ink. For example, non-image areas may be generally hydrophilic or oleophobic and image areas may be oleophilic.
The types of electronic parts whose manufacture may use a radiation-sensitive composition include printed wiring circuit boards, thick-and thin-film circuits, comprising passive elements such as resistors, capacitors and inductors; multichip devices; integrated circuits; and active semiconductor devices. The electronic parts may suitably comprise conductors, for example copper board; semiconductors, for example silicon, or germanium or Group III-V compound materials; and insulators, for example silica, as a surface layer with silicon beneath, with the silica being selectively etched away to expose portions of the silicon beneath. In relation to masks, a required pattern may be formed in the coating on the mask precursor, for example a plastics film, which is then used in a later processing step, in forming a pattern on, for example, a printing or electronic part substrate.
Conventionally, laser direct imaging methods (LDI) have been known which directly form an offset printing plate or printed circuit board on the basis of digital data from a computer. LDI offers the potential benefits of better line quality, just-in-time processing, improved manufacturing yields, elimination of film costs, and other recognized advantages. Examples of such methods include: (1) an electrophotographic method, (2) a photopolymerization method based on the combination of exposure by an Argon laser and post-heating, (3) a method in which a silver salt sensitive material is deposited on a photosensitive resin, (4) a method using a silver master and (5) a method in which a silicone rubber layer is decomposed by discharge breakdown or a laser beam.
However, in the electro-photographic method (1), processing such as charging, exposure and development are complicated, and the device used for the processing is complex and large. In method (2), a post-heating step is required. Further, a highly sensitive plate material is also required, and handling thereof in a light room is difficult. In methods (3) and (4), silver salts are used and thus the processing in these methods is complicated and the cost is high. Method (5) is a relatively complete method, but there remains a problem in that silicone dust remaining on the surface of the offset printing plate must be removed.
There has been remarkable development in the area of lasers. In particular, solid state lasers and semiconductor lasers having a luminous band from near infrared wavelengths to infrared wavelengths and which are small-sized and have a high energy output have become commercially available. These lasers are very useful as exposure light sources for exposure when LDI is required.
Thermally sensitive imaging elements are classified as compositions that undergo chemical transformation(s) in response to exposure to, and absorption of, suitable amounts of heat energy. The nature of thermally induced chemical transformation may be to ablate the composition, or to change the solubility of the composition in a particular developer, or to change tackiness of the surface, or to change the hydrophilicity or the hydrophobicity of the surface of the thermally sensitive layer. As such, selective heat exposure of predetermined areas (imagewise distribution of heat energy) of a film or layer formed of a thermally-sensitive composition has the capability of directly or indirectly producing a suitably imaged pattern which can serve as a resist pattern in printed circuit board fabrication, or in production of lithographic printing plates. Positive working systems based on novolak-diazoquinone resins are an imaging mainstay of the computer chip industry (see, e.g. R. R. Dammel, “Diazonaphthoquinone-based Resists”, Tutorial text No. 11, SPIE Press, Bellingham. WA, 993).
Compositions of light sensitive novolak-diazoquinone resins are also widely used in printing plate fabrication. The light sensitive diazonaphthoquinone derivatives (DNQ) added to or reacted with novolak resins (a phenol-formaldehyde condensation polymer) slow down the elution of the resin. A revised molecular mechanism of novolak-DNQ imaging materials has been suggested (A. Reiser, Journal of Imaging Science and Technology, Volume 42, Number 1, January/February 1998, pp. 15-22). This text teaches that the basic features of the imaging phenomena in novolak-diazonaphthoquinone compositions is the observed inhibition of dissolution of the resin, based on the formation of phenolic strings by the interaction of the strong hydrogen acceptor which acts as a solubility inhibitor with the OH groups of the resin. On exposure, the hydrogen bonding between the phenolic strings is severed during a reaction known as the Wolff rearrangement, which follows photolysis of the diazoquinone moiety of the inhibitor molecule. This rearrangement is not only very fast, but also highly exothermic. (ΔH° is at least −66 kcal/mol). The sudden appearance at the location of the solubility inhibitor of a heat pulse of that magnitude, causes a major temperature spike of not less than about 220° C. At the high temperature that is produced at the location of the solubility inhibitor, the phenolic string is severed from its anchor at the DNQ and becomes inactive (dispersed). This happens because it is no longer held together by the inductive effect of the solubility inhibitor.
This model may also explains the fact that a wide range of heat sensitive compositions based on novolak resins, wherein different types of inhibitors are incorporated, have been suggested. For example, positive-working direct laser addressable printing form precursors based on phenolic resins sensitive to UV, visible and/or infrared radiation have been described. See, for example, U.S. Pat. No. 4,708,925, U.S. Pat. No. 5,372,907 and U.S. Pat. No. 5,491,046.
In U.S. Pat. No. 4,708,925, the phenolic resin dissolution in alkaline solution is decreased by a radiation-sensitive onium salt, such as triphenylsulfoniumhexafluorophosphate, instead of DNQ, with the native solubility of the resin being restored upon photolytic decomposition of the onium salt. The onium salt composition is intrinsically sensitive to UV radiation and can be additionally sensitized to infrared radiation.
U.S. Pat. Nos. 5,372,907 and 5,491,046 utilize direct positive-working systems based on a radiation-induced decomposition of a latent Bronsted acid to increase the solubility of the resin matrix on imagewise exposure. The described compositions can be additionally utilized as negative-working systems with additional processing after imaging and predevelopment. The onium salts, quinonediazide compounds or the like are not necessarily compatible with the alkali aqueous solution soluble polymer compound or the material that absorbs light to generate heat. Thus, it is difficult to prepare a uniform coating solution and to obtain a uniform and stable material for laser direct imaging.
In U.S. Pat. Nos. 6,037,085 and 5,962,192 thermal laser-sensitive compositions are described based on azide-materials wherein a dye-substance is added to obtain the requisite sensitivity.
A wide range of thermally-induced compositions, useful as thermographic recording materials, are disclosed in patent GB 1,245,924, whereby the solubility of any given area of the imageable layer in a given solvent can be increased by heating of the layer by indirect exposure to a short duration high intensity visible light and/or infrared radiation transmitted or reflected from the background areas of a graphic original located in contact with the recording material. Several systems are described which operate by many different mechanisms and use different developing materials ranging from water to chlorinated organic solvents. Included in the range of aqueous developable compositions disclosed, are those that comprise a novolak type phenolic resin. The patent describes coated films of such resins that show increased solubility on heating. The compositions may contain heat-absorbing compounds such as carbon black or Milori Blue (C.I. Pigment Blue 27); these materials additionally color the images for their use as a recording medium.
Other compositions that include dissolution-inhibiting materials are described in the patent literature. Examples include WO 97/39894, WO 98/42507, WO99/08879, WO99/01795, WO99/21725, U.S. Pat. No. 6,117,623, U.S. Pat. No. 6,124,425, EP 940266 and WO 99/11458. However, the infrared dye, or the like, functions only as a dissolution-inhibiting agent in the non-exposed portions, and does not promote the dissolution of the binder resin in the exposed portions.
In U.S. Pat. No. 5,840,467 Kitatani et al describe a positive working image recording material, which comprises a binder, a light-to-heat converter substance capable of generating heat by the absorption of infrared rays or near infrared rays, and a heat-decomposable substance capable of substantially lowering the solubility of the material when the substance is in the undecomposed state. Specific examples of the heat-decomposable substance are diazonium salts and quinonediazide, both of which are known to practitioners in the field to generate gas upon heating to a suitable temperature. Specific examples of the binder include phenolic, acrylic and polyurethane resins. Various pigments and dyes are given as potential light-to-heat converter substances, including specifically cyanine dyes. The image recording material may be coated onto suitable substrates to create an imageable element. Elements so created may be imagewise irradiated with laser light and the irradiated areas removed with an alkaline developer.
Several materials capable of increasing the sensitivity of positive-working compositions have been described. Cyclic anhydrides as sensitizers are described in U.S. Pat. No. 4,115,128; examples include phthalic anhydride, succinic anhydride and pyromellitic anhydride. Phenols and organic acids have also been described in JP-A Nos. 60-88942 and 2-96755. Specific examples include bisphenol A, 2,3,4-trihydroxybenzophenone, 4-hydroxybenzophenone, p-toluenesulfonic acid, dodecylbenzenesulfonic acid, phenyl phosphate, diphenyl phosphate, benzoic acid, isophthalic acid, adipic acid, terephthalic acid, lauric acid, and ascorbic acid or the like.
In U.S. Pat. No. 6,232,031 Fromson describes a positive-working coating composition and a lithographic printing plate formed with a coating of that composition. The invention provides an infrared imageable lithographic printing plate having a phenolic resin coating containing an o-diazonaphthoquinone derivative coupled to or reacted with the resin and an infrared radiation-absorbing compound which also couples with the resin by hydrogen bonding to insolubilize the resin coating.